Maybe money does grow on trees. And in flower beds, too.

The annual return of the Philadelphia Flower Show, in full bloom through Sunday at the Pennsylvania Convention Center, is always a welcome harbinger of spring, especially when there's snow on the ground.

It's also a reminder of how much a public garden - even a temporary, indoor one like the Flower Show - contributes to the greening of the local economy as well as the landscape.

The Flower Show generates more than $61 million a year for the Philadelphia area economy and more than $8 million in local, state, and federal tax revenues, according to the Pennsylvania Horticultural Society, which runs the show.

While the Flower Show may be a spectacular example of gardening's economic clout, it's far from the only example. Public gardens within a 30-mile radius of Philadelphia have an economic impact of $256 million a year on the regional economy, according to a report to be released today by Greater Philadelphia Gardens.

GPG, a consortium of organizations that either operate or lend support to public gardens, arboreta, and historical landscapes, touts the Philadelphia area as "America's Garden Capital," a bold branding effort.

The nearly three dozen members of GPG span the region, from the Bowman's Hill Wildflower Preserve in New Hope to Longwood Gardens in Kennett Square to the Winterthur Museum, Garden and Library in Delaware.

The report on the gardens' financial impact, prepared for GPG by the Philadelphia economics consulting firm Econsult Solutions, found that they provide more than 1,500 jobs across the region, with earnings of $79 million. In addition, they have spent about $116 million on construction over the last three years.

Local gardens draw about 2.5 million visitors a year, more than either the Liberty Bell or Valley Forge National Park. That attendance is even better than the 1.9 million fans the Phillies drew last season.

A third of the visitors come from outside the region, giving a significant boost to the local tourist industry. They tend to be older and better off financially than the general population and willing to spend.

Two-thirds of the out-of-town visitors stay overnight in the area and spend an average of $145 a day on food and lodging.

The GPG report pointed out that the region should be particularly proud of attracting "discretionary visitors," many of them in the baby boomer generation, who could "easily substitute one destination for another."

When spring finally does come and you can walk in the garden again without boots, keep in mind that beneath the soothing, uplifting beauty, an economic engine is humming.